I just want to bring my help on this one.
Coquine can be something you say to a child (a girl in this case).
Mais quelle petite coquine!

But, in many cases it has a sexual meaning!
Picture two guys at a bar talking about their girlfriends : "Ma copine, c'est une vraie coquine!"
That means my girlfriend is all about sex, whe likes sex, or she likes to do uncommon things...
It's not gross or disrepectful, it's kind of sweet...

I could say it to my girlfriend, in the privacy of a couple, like "Quelle coquine!...", and she would probably like it...

It's hard to explain, but anyway don't say it to a grown up person, like your boss
hahaha "Mais quelle coquine vous êtes Madame la directrice!!!" That could be funny

Hope it helped!

Btw, I'm trying to find something similar in english, like the "coquine" you can say to your girlfriend....Anyone can help?